In the drill shaft industry, kelly bars are used to transmit the twisting torque from the rotary machinery to the bit or drill tool. This gives the bit or drill tool the ability to turn and excavate the earthen materials directly below itself.
The outside cross-section of a kelly bar is usually square, although other shaped kellys are sometimes used, such as round or hexagonal. The purpose of the cross-section is to enable torque to be transmitted from the rotary table to the cutting bit. During drilling operations, the kelly bushings or drivers remain on the rotary. Torque is applied from the rotary table through the kelly bushing, and thence to the kelly bar itself. The kelly bar is free to slide through the kelly bushing so that the drill can be rotated and simultaneously lowered or raised during drilling operations.
The drill shaft industry is normally associated with shaft excavations that range from 12 inch diameter to 10 feet or more diameter shafts. Depths range from several feet to 100' or more. The bigger the diameter and greater the depth the bigger drill rigs and the larger kelly bars need to be.
The kelly bar is usually raised and lowered by a single line usually made of braided wire rope or steel cable. This line is used to lower the kelly bar with the tool attached into the shaft and to raise the kelly bar and tool with excavated materials to the surface. A single line is usually adequate on depths up to 100 feet. When the shaft diameters are very large, which requires large, heavy drilling tools, and the kelly bar with the spoil exceed single line pull limits then multiple lines can be used.
A variation of a single kelly bar is the telescopic kelly bar. Telescopic kelly bars are used in the industry to achieve greater depths in drilling. It may comprise two sections, one inside the other. The outer bar may be made of square tubing and the upper inner bar may be made of solid square or possibly hollow square tubing. A single line hoist cable may be connected to the upper inner kelly bar by a swivel. The outer large kelly bar rests on the inner smaller kelly bar and drives the inner kelly bar. The smaller inner kelly bar is attached to the excavation tool such as an auger. As the auger proceeds deeper in the excavation, both kelly bars are extended downward until the top of the outer larger kelly bar descends to the top of the drive rollers or drive bushings. At the moment the top of the outer kelly bar hits the top of the drive rollers, the inner kelly bar will telescope or extend further downward from the outer bar. As the excavation progresses with each trip into the hole the telescoping of the kelly bar extends the auger to the bottom of the excavation until you reach the limit of the extension of the kelly bar.
Triple section bars and other multiple section bars are known. However, the middle bars are usually floating and the drill rig operator has little control over them. When these intermediate sections stick and no longer slidably telescope relative to the other sections, they may slide upwardly and possibly fall or slide down and cause damage.
Another configuration on telescopic kelly bars is to hold the upper outside bar with one hoist line and the lower inner bar with a separate hoist line. The drill operator coordinates the hoisting and lowering of the bars.
As the size and weight of structures increase, larger shafts are required. Large shafts for tunnels or mines have been excavated using mining techniques. It may be hard to drill the larger shafts due to the limitations of the currently available equipment. Two factors that make the use of traditional drill shaft techniques for very large and deep excavations difficult are torque requirements and hoisting requirements. Where a typical drill shaft is less than 10 feet in diameter, tunnel shafts may go up to 30 feet in diameter and a depth greater than 200 feet. These larger dimensions call for larger and longer kelly bars so they can transmit the required torque to extended depths. Larger dimensions call for longer and heavier kelly bars. The use of these larger kelly bars means that single line pulls on cranes may not be adequate. The weight of a large kelly bar that transmits high torque to great depths can be greater than 30,000 lbs. If we add to this the weight of the tool and the muck or the spoil being lifted from the excavation, a total weight greater than 50,000 lbs. may be handled by the crane and cable supporting the kelly bar and tool. In order to handle the increased loads, a multiple part line may be implemented. The use of a multiple part line on a deep shaft would be impractical on a conventional telescoping kelly bar. A reason for this is that the shieve block connected to the upper inner kelly might not be able to extend and descend through the outer kelly bar unless the outer kelly bar has an extremely large bore or inside cross-section.
The present invention includes a reverse telescopic multi-section kelly bar capable of digging hundreds of feet deep necessary for the large diameters associated with tunneling or other large diameter deep shaft requirements. An objective of the present invention is to solve some of the problems associated with drilling large diameter deep shafts. The lower outer bar of the present invention is rigid and is attached to the drill tool, a straight hole may be drilled when a drill tool is used that is slightly larger in diameter than the largest cross-section of the lower outer bar. This could not be accomplished with a conventional telescopic kelly bar because the tool attaches to the smaller bar. Once the lower outer bar on a conventional telescopic kelly bar is fully extended it can no longer follow the drill tool, thus losing the lower outer bar rigidly at the top of the tool and losing an excavation that is slightly bigger than the longest cross-section of the kelly bar attached to the tool. Another objective of this invention is to allow drilling near perfect straight shafts. Another objective of this invention is to provide the operator full control of the kelly bars. An additional objective of this invention is the elimination of uncontrolled floating of kelly bars. Another objective of this invention is to allow handling of large muck quantities. These and other objects of the invention will be apparent to those skilled in this art from the following detailed description of a preferred embodiment of the invention.